Plants leaves are sealed with a gas-tight wax layer to prevent water loss. Plants breathe through microscopic pores called stomata (Greek for mouths) on the surfaces of leaves. Over 40% of the carbon dioxide, CO2, in the atmosphere passes through stomata each year, as well a water volume twice that of the whole atmosphere. As the key conduits for CO2 uptake and water evaporation, stomata are critical for both our climate and plant productivity. Thus, not surprisingly, the total number and distribution of stomata are strictly regulated by plants to optimize photosynthesis while minimizing water loss. The mechanisms for such regulation have remained elusive.

Plants are very sensitive to light conditions, in part due to a signal that activates some special photoreceptors that regulate growth, metabolism, and physiological development. Scientists believe that these light signals control plant growth and development by activating or inhibiting plant hormones. New research from Carnegie plant biologists has altered the prevailing theory on how light signals and hormones interact. Their findings could have implications for food crop production.

Researchers at the Carnegie Institution’s Department of Plant Biology have discovered a key missing link in the so-called signaling pathway for plant steroid hormones (brassinosteroids). Many important signaling pathways are relays of molecules that start at the cell surface and cascade to the nucleus to regulate genes. This discovery marks the first such pathway in plants for which all the steps of the relay have been identified. Since this pathway shares many similarities with pathways in humans, the discovery not only could lead to the genetic engineering of crops with higher yields, but also could be a key to understanding major human diseases such as cancer, diabetes, and Alzheimer’s.